Farhad Arbab

Reo: a channel-based coordination model for component composition

In this paper, we present Reo, which forms a paradigm for composition of software components based on the notion of mobile channels. Reo is a channel-based exogenous coordination model in which complex coordinators, called connectors, are compositionally built out of simpler ones. The simplest connectors in Reo are a set of channels with well-defined behaviour supplied by users. Reo can be used as a language for coordination of concurrent processes, or as a ‘glue language’ for compositional construction of connectors that orchestrate component instances in a component-based system. The emphasis in Reo is just on connectors and their composition, and not on the entities that connect to, communicate and cooperate through these connectors. Each connector in Reo imposes a specific coordination pattern on the entities (for example, components) that perform I/O operations through that connector, without the knowledge of those entities. Channel composition in Reo is a very powerful mechanism for construction of connectors. We demonstrate the expressive power of connector composition in Reo through a number of examples. We show that exogenous coordination patterns that can be expressed as (meta-level) regular expressions over I/O operations can be composed in Reo out of a small set of only five primitive channel types.

The IWIM Model for Coordination of Concurrent Activities

Exploiting the full potential of massively parallel systems requires programming models that explicitly deal with the concurrency of cooperation among very large numbers of active entities that comprise a single application. In practice, the concurrent applications of today essentially use a set of ad hoc templates to coordinate the cooperation of their active components. This shows the lack of proper coordination languages that can be used to explicitly describe complex cooperation protocols in terms of simple primitives and structuring constructs.

A Coinductive Calculus of Component Connectors

Reo is a recently introduced channel-based model for coordination, wherein complex coordinators, called connectors, are compositionally built out of simpler ones. Using a more liberal notion of a channel, Reo generalises existing dataflow networks. In this paper, we present a simple and transparent semantical model for Reo, in which connectors are relations on timed data streams. Timed data streams constitute a characteristic of our model and consist of twin pairs of separate data and time streams. Furthermore, coinduction is our main reasoning principle and we use it to prove properties such as connector equivalence.

Enterprise architecture: Management tool and blueprint for the organisation

This is an editorial to a special issue of ISF on enterprise architecture.We define the concept of enterprise architecture, notivate its importance, and then introduce the papers in this special issue.

Abstract behavior types: a foundation model for components and their composition

The notion of Abstract Data Type (ADT) has served as a foundation model for structured and object oriented programming for some thirty years. The current trend in software engineering toward component based systems requires a foundation model as well. The most basic inherent property of an ADT, i.e., that it provides a set of operations, subverts some highly desirable properties in emerging formal models for components that are based on the object oriented paradigm.We introduce the notion of Abstract Behavior Type (ABT) as a higher-level alternative to ADT and propose it as a proper foundation model for both components and their composition. An ABT defines an abstract behavior as a relation among a set of timed-data-streams, without specifying any detail about the operations that may be used to implement such behavior or the data types it may manipulate for its realization. The ABT model supports a much looser coupling than is possible with the ADTs operational interface, and is inherently amenable to exogenous coordination. We propose that both of these are highly desirable, if not essential, properties for models of components and their composition.To demonstrate the utility of the ABT model, we describe Reo: an exogenous coordination language for compositional construction of component connectors based on a calculus of channels. We show the expressive power of Reo, and the applicability of ABT, through a number of examples.

An algorithm for generating NC tool paths for arbitrarily shaped pockets with islands

In this paper we describe algorithms for generating NC tool paths for machining of arbitrarily shaped 2 l/2 dimensional pockets with arbitrary islands. These pocketing algorithms are based on a new offsetting algorithm presented in this paper. Our offsetting algorithm avoids costly two-dimensional Boolean set operations, relatively expensive distance calculations, and the overhead of extraneous geometry, such as the Voronoi diagrams, used in other pocketing algorithms.

Connector colouring I: Synchronisation and context dependency

Reo is a coordination model based on circuit-like connectors which coordinate components through the interplay of data flow, synchronisation and mutual exclusion, state, and context-dependent behaviour. This paper proposes a scheme based on connector colouring for determining the behaviour of a Reo connector by resolving its context dependent synchronisation and mutual exclusion constraints. Colouring a Reo connector in a specific state with given boundary conditions (I/O requests) provides a means to determine the routing alternatives for data flow. Our scheme has the advantage over previous models in that it is simpler to implement and that it models Reo connectors more closely in terms of their envisaged semantics than existing formal models.

Towards a language for coherent enterprise architecture descriptions

A coherent description of architectures provides insight, enables communication among different stakeholders and guides complicated (business and ICT) change processes. Unfortunately, so far no architecture description language exists that fully enables integrated enterprise modeling. In this paper we focus on the requirements and design of such a language. This language defines generic, organization-independent concepts that can be specialized or composed to obtain more specific concepts to be used within a particular organisation. It is not our intention to re-invent the wheel for each architectural domain: wherever possible we conform to existing languages or standards such as UML. We complement them with missing concepts, focusing on concepts to model the relationships among architectural domains. The concepts should also make it possible to define links between models in other languages. The relationship between architecture descriptions at the business layer and at the application layer (business-IT alignment) plays a central role.

Towards Using Reo for Compliance-Aware Business Process Modeling

Business process modeling and implementation of process supporting infrastructures are two challenging tasks that are not fully aligned. On the one hand, languages such as Business Process Modeling Notation (BPMN) exist to capture business processes at the level of domain analysis. On the other hand, programming paradigms and technologies such as Service-Oriented Computing (SOC) and web services have emerged to simplify the development of distributed web systems that underly business processes. BPMN is the most recognized language for specifying process workflows at the early design steps. However, it is rather declarative and may lead to the executable models which are incomplete or semantically erroneous. Therefore, an approach for expressing and analyzing BPMN models in a formal setting is required. In this paper we describe how BPMN diagrams can be represented by means of a semantically precise channel-based coordination language called Reo which admits formal analysis using model checking and bisimulation techniques. Moreover, since additional requirements may come from various regulatory/legislative documents, we discuss the opportunities offered by Reo and its mathematical abstractions for expressing process-related constraints such as Quality of Service (QoS) or time-aware conditions on process states.

Abstract Behavior Types: A Foundation Model for Components and Their Composition

The notion of Abstract Data Type (ADT) has served as a foundation model for structured and object oriented programming for some thirty years. The current trend in software engineering toward component based systems requires a foundation model as well. The most basic inherent property of an ADT, i.e., that it provides a set of operations, subverts some highly desirable properties in emerging formal models for components that are based on the object oriented paradigm. We introduce the notion of Abstract Behavior Type (ABT) as a higher-level alternative to ADT and propose it as a proper foundation model for both components and their composition. An ABT defines an abstract behavior as a relation among a set of timed-data-streams, without specifying any detail about the operations that may be used to implement such behavior or the data types it may manipulate for its realization. The ABT model supports a much looser coupling than is possible with the ADTs operational interface, and is inherently amenable to exogenous coordination. We propose that both of these are highly desirable, if not essential, properties for models of components and their composition. To demonstrate the utility of the ABT model, we describe Reo: an exogenous coordination language for compositional construction of component connectors based on a calculus of channels. We show the expressive power of Reo, and the applicability of ABT, through a number of examples.